Semiconductor device

Abstract

There is provided a semiconductor device in which gate electrodes of both an n-channel field effect transistor and a p-channel field effect transistor constituting a complementary field effect transistor are made of the same material and threshold voltages of both are sufficiently lowered. In the semiconductor device including an n-channel MOSFET and a p-channel MOSFET which constitute a CMOS structure, the gate electrode of the n-channel MOSFET and the gate electrode of the p-channel MOSFET are made of the same material, at least a part of a channel region of the n-channel MOSFET is formed in a strained Si layer, at least a part of a channel region of the p-channel MOSFET is formed in an SiGe layer, the work function of the material making the gate electrodes is higher than an energy difference between the conduction band edge of the strained Si layer and the vacuum level, and is lower than an energy difference between the valence band edge of the SiGe layer and the vacuum level.

What is claimed is:  
     
       1. A semiconductor device comprising: 
       a semiconductor substrate;  
       an n-channel field effect transistor formed on the semiconductor substrate;  
       and a p-channel field effect transistor formed on the semiconductor substrate, the n-channel field effect transistor and the p-channel field effect transistor constituting a complementary field effect transistor,  
       wherein a gate electrode of the n-channel field effect transistor and a gate electrode of the p-channel field effect transistor are made of a same material,  
       wherein a channel region of the n-channel field effect transistor is made of a material which contains at least of Si and in which an energy difference between a conduction band edge and a vacuum level is higher than that of bulk Si, and a channel region of the p-channel field effect transistor is made of a material which contains at least of Si and in which an energy difference between a valence band edge and the vacuum level is lower than that of bulk Si, and  
       wherein a work function of the material making the gate electrodes is higher than the energy difference between the conduction band edge of the material making the channel region of the n-channel field effect transistor and the vacuum level, and is lower than the energy difference between the valence band edge of the material making the channel region of the p-channel field effect transistor and the vacuum level.  
     
     
       2. A semiconductor device according to  claim 1 , wherein tensile stress is introduced into the material making the channel region of the n-channel field effect transistor. 
     
     
       3. A semiconductor device according to  claim 1 , wherein compressive stress is introduced into the material making the channel region of the p-channel field effect transistor. 
     
     
       4. A semiconductor device according to  claim 1 , wherein the material making the channel region of the n-channel field effect transistor is strained Si. 
     
     
       5. A semiconductor device according to  claim 1 , wherein the material making the channel region of the p-channel field effect transistor is SiGe. 
     
     
       6. A semiconductor device according to  claim 1 , wherein the Fermi level E F  of the gate electrode material is ( 4 E v2  +E c1 )/5 or less and (E v2  + 4 E c1 )/5 or less, E v2  is the valence band edge of the material making the channel region of the p-channel field effect transistor and E c1  is the conduction band edge of the material making of the channel region of the n-channel field effect transistor. 
     
     
       7. A semiconductor device according to  claim 1 , wherein the Fermi level E F  of the gate electrodematerial is substantially (E v2  +E c1 )/2, E v2  is the valence band edge of the material making the channel region of the p-channel field effect transistor and E c1  is the conduction band edge of the material making of the channel region of the n-channel field effect transistor. 
     
     
       8. A semiconductor device according to  claim 1 , wherein E c1  of the channel material of the n-channel MOSFET is higher than (E v0  + 9 E c0 )/10 and not higher than (E v0  +E c0 )/2, E v0  is the valence band edge of the bulk Si and E c0  is the conduction band edge of the bulk Si. 
     
     
       9. A semiconductor device according to  claim 1 , wherein E v2  of the channel material of the p-channel MOSFET is not less than (E v0  +E c0 )/2 and less than ( 9 E v0  +E c0 )/10, E v0  is the valence band edge of the bulk Si and E c0  is the conduction band edge of the bulk Si. 
     
     
       10. A semiconductor device comprising: 
       a semiconductor substrate;  
       an n-channel field effect transistor formed on the semiconductor substrate; and  
       a p-channel field effect transistor formed on the semiconductor substrate, the n-channel field effect transistor and the p-channel field effect transistor constituting a complementary field effect transistor,  
       wherein a gate electrode of the n-channel field effect transistor and a gate electrode of the p-channel field effect transistor are made of a same material,  
       wherein at least a part of a channel region of the n-channel field effect transistor is formed in a strained Si layer,  
       wherein at least a part of a channel region of the p-channel field effect transistor is formed in a first SiGe layer, and  
       wherein a work function of the material making the gate electrodes is higher than an energy difference between a conduction band edge of the strained Si layer and a vacuum level, and is lower than an energy difference between a valence band edge of the first SiGe layer and the vacuum level.  
     
     
       11. A semiconductor device according to  claim 10 , wherein the n-channel field effect transistor includes a second SiGe layer which has the same composition ratio as the first SiGe layer and is disposed between the semiconductor substrate and the strained Si layer, and tensile stress is introduced into the strained Si layer from the second SiGe layer. 
     
     
       12. A semiconductor device according to  claim 10 , wherein the n-channel field effect transistor includes a second SiGe layer which has a Ge concentration higher than the first SiGe layer and is disposed between the semiconductor substrate and the strained Si layer, 
       the p-channel field effect transistor includes a third SiGe layer which has the same composition ratio as the second SiGe layer and is disposed between the semiconductor substrate and the first SiGe layer,  
       tensile stress is introduced into the strained Si layer from the second SiGe layer, and  
       compressive stress is introduced into the first SiGe layer from the third SiGe layer.  
     
     
       13. A semiconductor device according to  claim 12  wherein the p-channel field effect transistor includes a Si layer between the first SiGe layer and the third SiGe layer. 
     
     
       14. A semiconductor device according to  claim 12 , wherein the first SiGe layer composes Si 1−x Ge x  and the second SiGe layer composes Si 1−y Ge y  (y>x). 
     
     
       15. A semiconductor device according to  claim 1 , wherein the gate electrode is made of a material selected from the group consisting of metal, doped p-type polycrystalline Ge, and doped p-type polycrystalline SiGe. 
     
     
       16. A semiconductor device according to  claim 10 , wherein the gate electrode is made of a material selected from the group consisting of metal, doped p-type polycrystalline Ge, and doped p-type polycrystalline SiGe. 
     
     
       17. A semiconductor device according to  claim 1 , further comprising an insulating film between the semiconductor substrate and the complementary field effect transistor. 
     
     
       18. A semiconductor device according to  claim 10 , further comprising an insulating film between the semiconductor substrate and the complementary field effect transistor. 
     
     
       19. A semiconductor device comprising: 
       a semiconductor substrate;  
       an n-channel field effect transistor formed on the semiconductor substrate; and  
       a p-channel field effect transistor formed on the semiconductor substrate, the n-channel field effect transistor and the p-channel field effect transistor constituting a complementary field effect transistor,  
       wherein a gate electrode of the n-channel field effect transistor and a gate electrode of the p-channel field effect transistor are made of a same material, and  
       wherein one of the n-channel field effect transistor and the p-channel field effect transistor includes a first semiconductor layer in which at least a part of a channel region is formed, the other of the n-channel field effect transistor and the p-channel field effect transistor includes a second semiconductor layer in which at least a part of a channel region is formed and a third semiconductor layer as its under layer, and the first semiconductor layer and the third semiconductor layer are made of a same material.  
     
     
       20. A semiconductor device according to  claim 19 , further comprising an insulating film between the semiconductor substrate and the complementary field effect transistor. 
     
     
       21. A semiconductor device according to  claim 19 , wherein a work function of the material making the gate electrode is higher than an energy difference between a conduction band edge of a material making the channel region of the n-channel field effect transistor and a vacuum level, and is lower than an energy difference between a valence band edge of a material making the channel region of the p-channel field effect transistor and the vacuum level.